1. Field of the Invention
The present invention relates to a vibration actuator drive device which uses a vibration actuator to generate relative motion of relative motion members, and more particularly, the present invention relates to a vibration actuator drive device which generates relative motion of relative motion members on a curved locus between relative motion members using a linear type of vibration actuator. Moreover, the present invention relates to a lens barrel using a vibration actuator drive device for driving a lens group in an optical axis direction to change the focal point or focal distance of a photographic optical system.
2. Description of the Related Art
Vibration actuators are conventionally used as a motive power source for driving lenses because vibration actuators have features such as good control characteristics, noiselessness, and high torque. For example, vibration actuators are conventionally used in lens barrels as the motive power source for an automatic focus adjustment mechanism. Moreover, vibration actuators are also used as the motive power source for a so-called power zoom to perform the electromotive adjustment of focal distance in a zoom lens barrel. For example, Japanese Laid-Open Patent Publication JP-A-59-111117 discloses a lens barrel which uses an annular vibration actuator (referred to hereinbelow as an "annular type vibration actuator"). The annular type vibration actuator is a rotary type of vibration actuator which outputs a rotary drive force.
Furthermore, linear types of vibration actuators are known which output a rectilinear drive force. For example, the constitution and load characteristics of a linear type vibration actuator are described in "Piezoelectric Linear Motor with Optical Pickup Motion as Object" (Yoshiroh Tomikawa et al.: 5th Dynamics Symposium Relating to Electromagnetic Force, Collected Papers, pp. 393-398). The linear type of vibration actuator consists of an elastic member having a flat plate form and an electromechanical converting element brought into contact with the elastic member. By applying an alternating current to the electromechanical converting element, a longitudinal vibration and a bending vibration are generated in the elastic member, thereby causing an elliptical vibration to be generated in the surface of the elastic member.
Japanese Laid-Open Patent Publication JP-A-8-211279 discloses a lens barrel having both an annular type of vibration actuator to drive a focus adjustment lens group for adjusting the focus, and a linear type of vibration actuator to drive a focal distance adjustment lens group for adjusting the focal distance. FIG. 31 is a cross-sectional diagram of the lens barrel disclosed in JP-A-8-211279. As shown in FIG. 31, the lens barrel includes a vibration actuator 210 located on an outer circumferential side of a focus adjustment lens group L201. The vibration actuator 210 is an annular type of vibration actuator consisting of a stator 211 and a rotor 212. In operation, a rotary tube 202 is driven to rotate by the rotary motion of the rotor 212. The rotation of the rotary tube 202 is transmitted to a frame 206 of the focus adjustment lens group L201 via a key groove 202a and a key 206a, thereby causing the frame 206 to rotate integrally with the rotary tube 202. Furthermore, the rotary motion of the frame 206 is converted into a rectilinear motion in the optical axis direction by a helicoid 209 coupled to a fixed tube 201. As a result, the frame 206 and the focus adjustment lens group L201 move in the optical axis direction.
Furthermore, as shown in FIG. 31, a linear type of vibration actuator 205 is located on an outer circumferential side of a focal length adjustment lens group L202. The linear type vibration actuator 205 is in contact with a flat unit 207a disposed on the outer circumferential surface of a frame 207. When the vibration actuator 205 is driven, a driving force in the optical axis direction is applied to the flat unit 207a. As a result, the frame 207 and the focal length adjustment lens group L202 move in the optical axis direction, guided by a linear guide 208 which penetrates through the frame 207.
However, the following problems occur in the prior art lens barrels described above. Firstly, when a frame of a photographic optical system is rectilinearly driven in the optical axis direction using a linear type of vibration actuator, the position setting accuracy of the frame is decided by a minimum distance which the vibration actuator can cause the frame to move (referred to hereinbelow as a "drive unit"). Accordingly, the accuracy of focus adjustment or focal length adjustment cannot be increased above the drive unit of the linear type of vibration actuator.
Moreover, in an annular type of vibration actuator, high surface accuracy is required in the contact surfaces of both the stator and the rotor. The surface accuracy does not particularly become a problem in a small type of vibration actuator. However, the difficulty of maintaining a suitable surface accuracy in the contact surfaces becomes a problem in a vibration actuator used in a lens barrel because the stator and rotor come to have a large diameter on the same order as the diameter of the lens barrel.